This invention relates to a developer material coating apparatus for coating a developer material on a support member such as a plain paper or the like to form an image forming medium.
In a conventional image forming apparatus, a particular paper produced in a . paper manufacturing company has been necessarily used as an image forming medium for forming an image thereon. Accordingly, in the conventional image forming apparatus, it has been impossible for an user to form the image on a support member such as a plain paper which is freely selected by the user, and further it has been impossible for the user to coat a developer material on the support member to form an image forming medium.
In view of the above disadvantage of the conventional image forming apparatus, there has been proposed an image forming apparatus in which microcapsules encapsulating dye precursor and having a mechanical strength variable in accordance with intensity of light irradiated thereto. This image forming apparatus is described in the co-pending U.S. Pat. Application No. 253,614 filed on Oct. 5, 1988 which has been commonly assigned to the assignee of this application. In this image forming apparatus, a microcapsule sheet on which the microcapsules are carried and to which light has been irradiated in accordance with an image information is closely contacted with an image forming medium which is formed by coating the surface of a support member such as a plain paper or the like with a developer material, the support member being freely selected by the user, and then the contacted microcapsule sheet and the support member are subjected to a pressure-development. In the pressure development process, those microcapsules which have a low mechanical intensity are ruptured and then the dye precursor issued from the ruptured microcapsules is reacted with the developer material coated on the support member, so that an image is formed on the support member. In the coating process for coating the developer material on the support member, the developer material is positively charged with contact or friction of the developer material with a developing sleeve or other members in a charging unit, and an electrode which is applied with a voltage having the opposite polarity to the developer material (for example, a voltage having a negative polarity) is disposed at the rear surface side of the support member. An electric field portion for electrically attracting the charged developer material to the support member is formed between the charging unit and the electrode. Accordingly, the charged developer material is electrically attached to the whole front surface of the support member and is coated thereon.
In the image forming apparatus thus constructed, the charged developer material is firmly attached to the front surface of the support member when it is electrically attached thereto (that is , the developer material is disposed in the electric field portion and an electrostatic force is applied to the charged developer material by the electrode). However, the charged material is injected with charges from the support member and an attaching force of the developer material to the support member is reduced immediately when it is fed out of the electric field portion. Further, the support member absorbs moisture in a highly-moist atmosphere and an insulating property of the support member is degraded, so that a transfer coefficient (a coefficient of transferring and adsorbing the developer material to the support member) is lowered.
The lowering of the attaching capability (force) of the developer material to the support member causes the conventional image forming apparatus to suffer from the following disadvantages. The developer material on the support member is liable to be detached from the support member when fed out of the electric field portion. Further, in the pressure-developing process in which the microcapsule sheet and the support member having the developer material thereon are closely contacted with each other under pressure, the developer material is liable to be attached to the microcapsule sheet with no chromogenic reaction As a result, no image is formed on the support member, or an image is not wholly formed on the image member(that is, a part (some pixels) of the image is not formed on the support member.